In advanced wireless communication systems, orthogonal frequency division multiplexing (OFDMA) is a popular and efficient multiple access technology. Data can be transmitted in two types of resources in OFDMA: contiguous resources and diversity resources. When using diversity resources, OFDM tones in a particular physical channel should be distributed over the entire frequency band so that frequency diversity can be achieved for that channel. A resource unit for diversity mode transmission is usually created by choosing a certain number of tones from different parts of the frequency band. For example, in the Institute for Electronic and Electrical Engineers (IEEE) P802.16m/D2, the process of tone-selection is done in the frequency domain to form blocks of 16 tones and the process is performed symbol by symbol to form 16 tone by 6 symbol resource units.
This general procedure can become a problem if the process is the same or almost the same symbol by symbol. The reason is that some physical channels are small in size and do not occupy the entire resource unit. The channel can only occupy very few tones per symbol. In this case, if the tone-selection process is the same over time (i.e. over different symbols), the channel may be composed of tones with little or no frequency diversity at all.
Thus, a strong need exists for techniques that use an improved subcarrier permutation to achieve high frequency diversity of OFDMA systems.
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